The field of soil conditioners was changed in the 1950's by the introduction of synthetic polymers, especially linear polymers and copolymers of polyacrylamide (PAM) and poly(acrylic acid). These soil binding and soil flocculating agents amended soil via aggregation of particulates and thereby stabilized soil surface structure. By the 1980's and early 1990's, significant research had established PAM and its copolymers as a viable soil conditioner.
Currently, PAM is added to irrigation water as a means of treating irrigated soil. Some studies indicate that the use of PAM reduces irrigation runoff as much as 97% while improving water infiltration. In operation, high molecular weight anionic PAM is added to irrigation water at very low concentration (at 2-10 g m-3, or 2-10 ppm) during the first several hours of irrigation. Soil-amending polymers are generally dissolved in irrigation water at doses of 2 to 20 parts per million, which converts to about 2 to 10 lbs per acre. Erosion is reduced because the polymer additive treats the soil that is directly in contact with the moving water; i.e., soil structure is improved in the all-important 1-5 mm thick layer at the soil/water interface of the field surface contacted by flowing water. During furrow irrigation, these polymers bind to soil particles causing them to settle out and “seal” the furrow from further erosion.
Since toxic pesticides and herbicides are transported via soil sediment to open waterways, preventing sediment runoff also prevents chemical runoff. PAM has been shown to sequester biological and chemical contaminants in runoff sediment, thereby providing significant potential for reduced spread of phytopathogens, animal coliforms and other organisms of public health concern.
In addition to conventional soil erosion control, PAM is also used in a wide variety of other applications. For example, PAM is effective in sealing unlined water-delivery canals to reduce water seepage or infiltration losses. Other applications include controlling dust emissions at (for example) construction sites, rural roads, deforested areas—especially after fires or natural disasters, and at temporary helicopter landing pads and military air strips.
However, there are multiple concerns associated with the widespread use of PAM. In many applications PAM may be difficult to work with and apply effectively. High molecular weight polymers like PAM exhibit corresponding high viscosities and typically form gelatinous masses. These masses are difficult to manipulate and meter into (for example) irrigation water or other carrier mediums.
The main environmental concern revolves around polymer purity, and issues related to biodegradation and/or accumulation. PAM is conventionally derived from petroleum and therefore biodegrades very slowly. The long-term effect of PAM on living organisms in the soil application context is relatively unknown. The base monomer, acrylamide, is a hazardous, reactive monomer that is a known neurotoxin and suspected carcinogen. Although PAM providers take steps to ensure that levels of potentially dangerous monomers are well within safety limits, it is evident that alternative materials would broaden the potential market for soil additives.
Potential alternatives to PAM, such as polysaccharides, amino acid polymers and other modified biopolymers have been introduced to provide soil amending properties similar to PAM. These alternatives rapidly degrade and provide marketing advantages due to the relative safety of natural compounds. Among these are natural and modified polysaccharides, polyamino acids (U.S. Pat. Nos. 7,595,002 and 7,595,007), starch xanthate, and chitosan. However, these alternatives are relatively expensive to produce—particularly in large quantities.
The need exists for additional PAM alternatives that either reduce or eliminate the use of PAM. The alternatives should be at least competitive with (and preferably less expensive) than conventional PAM applications. The current invention comprises a formulation of novel polysaccharides, specifically complex galactomannon-rich polysaccharides derived from succulent plants. Succulent plant material suitable for use in the current formulation is available as an inexpensive and plentiful agricultural by-product. Application of the formulation results in soil flocculation properties comparable to PAM, without the potential effects associated with a synthetic petroleum product. The biopolymers and additives of the current invention improve the handling characteristics and reduce the cost and environmental impacts of conventional commercially-available flocculants.